Hi Guys,
I'm working on building a film scanning machine, I have a pretty good idea of how the mechanics
should work but I don't have a whole lot of experience with circuits so it would be amazing if anyone here could offer some advice. I'm hoping in explaining my idea someone could help me figure out what specific components I should buy and the basics of how it would be wired.
The idea is based on this machine:
http://cdn.instructables.com/FJB/5PAA/HRWNC86T/FJB5PAAHRWNC86T.LARGE.jpg
which is a movie film scanner for 3 different formats - super 8mm, 16mm and 35mm, i'm basically just using the same platform structure of the kinograph but using other software to control the camera settings. The camera is triggered to capture an image by my own design for the circuitry.
Essentially I want the scanner setup to be a 'projector' of sorts, except it can take 3 different film gauges, and it doesn't project an image, only advances one frame at a time, stops it for a moment - illuminated by a LED light - triggers the camera, then advances to the next, etc. The scanner should advance the film across the LED at 3-4 frames per second. Since all 3 film gauges are different sizes, i will need to be able to switch between 3 motor speeds. They don't have to be 3 frames per second exactly since the camera is triggered when the film is advanced sufficiently for each frame.
In my mind the circuitry would be something like as follows:
a) a laser shines through the sprocket holes onto a light sensor. It has adjustable height depending on the film gauge.
b) Depending on the film format, a 2 way switch is moved to one of two 'counters'. One counts to
1 (the amount of sprockets per frame for super 8 and 16mm film), the other counts to 4 (the amount
of sprockets per 35mm frame).
c) Then (somehow), a counter resets once it reaches its limit (1 or 4), and the act of reseting sends 2 signals:
1 to trigger a Machine Vision camera, the other signal instantly stops the take-up motor, maybe including some sort of breaking mechanism, since the timing is critical.
d) This pause in the take-up motor is perhaps a timer (preferably with easily changeable times, but
probably set around 1/50th of a second for the sake of argument), once the timer is up, the motor starts moving again and the whole cycle continues.
My main concerns are:
1) Should I use stepper motors or continuous motors? The issue is around how to ensure once the desired sprocket is counted, that the motor (and hence the film) stops immediately. In terms of choice of motor my understanding is that a stepper motor might not stop in the same position for each frame. It seems most stepper motors are around 200 discrete steps per full revolution, which might not have the level of accuracy/control needed for all 3 film gauges, since the super 8 film will need smaller increments than 35mm film to advance.
On the other hand, my understanding is that whilst a continuous motor has infinite positions it can stop
in, that once it gains momentum, cutting the power won't necessarily stop it dead in it's tracks, that it will
slowly come to a halt. Maybe this isn't such an issue since the motor will be stopping and starting 3 or 4 times a second? Bare in mind the smallest in differences is enough to cause the resulting video file to shake all over the place and/or be out of frame.
2) Can I make a counting device reset at a preset number, and send a signal upon such a reset? Is this easy enough or perhaps there's an easier gadget to get the same effect? Perhaps for the 4 counts for 35mm for e.g., could I have 4 gates of some sort in series that close one by one, thus completing the circuit upon the 4th sprocket signal?
3) How to power and control the speed of the take-up motor, with 3 or so speeds? Also how to power and control the non-takeup motor.
4) BONUS if anyone here can help though it might be the wrong forum: Do you think I can get away with using a rolling shutter machine vision camera or do I really need a global shutter? Since it's only 3 or 4 fps, and i'm guessing the camera shutter can be set around 1/100th of a second shutter speed, and the film won't be moving
when the image is taken, I feel it should do the trick? Otherwise i'm looking at spending over double to get an equivalent camera with a global shutter.
Any thoughts would be great appreciated!
Cheers,
Mr.We
I'm working on building a film scanning machine, I have a pretty good idea of how the mechanics
should work but I don't have a whole lot of experience with circuits so it would be amazing if anyone here could offer some advice. I'm hoping in explaining my idea someone could help me figure out what specific components I should buy and the basics of how it would be wired.
The idea is based on this machine:
http://cdn.instructables.com/FJB/5PAA/HRWNC86T/FJB5PAAHRWNC86T.LARGE.jpg
which is a movie film scanner for 3 different formats - super 8mm, 16mm and 35mm, i'm basically just using the same platform structure of the kinograph but using other software to control the camera settings. The camera is triggered to capture an image by my own design for the circuitry.
Essentially I want the scanner setup to be a 'projector' of sorts, except it can take 3 different film gauges, and it doesn't project an image, only advances one frame at a time, stops it for a moment - illuminated by a LED light - triggers the camera, then advances to the next, etc. The scanner should advance the film across the LED at 3-4 frames per second. Since all 3 film gauges are different sizes, i will need to be able to switch between 3 motor speeds. They don't have to be 3 frames per second exactly since the camera is triggered when the film is advanced sufficiently for each frame.
In my mind the circuitry would be something like as follows:
a) a laser shines through the sprocket holes onto a light sensor. It has adjustable height depending on the film gauge.
b) Depending on the film format, a 2 way switch is moved to one of two 'counters'. One counts to
1 (the amount of sprockets per frame for super 8 and 16mm film), the other counts to 4 (the amount
of sprockets per 35mm frame).
c) Then (somehow), a counter resets once it reaches its limit (1 or 4), and the act of reseting sends 2 signals:
1 to trigger a Machine Vision camera, the other signal instantly stops the take-up motor, maybe including some sort of breaking mechanism, since the timing is critical.
d) This pause in the take-up motor is perhaps a timer (preferably with easily changeable times, but
probably set around 1/50th of a second for the sake of argument), once the timer is up, the motor starts moving again and the whole cycle continues.
My main concerns are:
1) Should I use stepper motors or continuous motors? The issue is around how to ensure once the desired sprocket is counted, that the motor (and hence the film) stops immediately. In terms of choice of motor my understanding is that a stepper motor might not stop in the same position for each frame. It seems most stepper motors are around 200 discrete steps per full revolution, which might not have the level of accuracy/control needed for all 3 film gauges, since the super 8 film will need smaller increments than 35mm film to advance.
On the other hand, my understanding is that whilst a continuous motor has infinite positions it can stop
in, that once it gains momentum, cutting the power won't necessarily stop it dead in it's tracks, that it will
slowly come to a halt. Maybe this isn't such an issue since the motor will be stopping and starting 3 or 4 times a second? Bare in mind the smallest in differences is enough to cause the resulting video file to shake all over the place and/or be out of frame.
2) Can I make a counting device reset at a preset number, and send a signal upon such a reset? Is this easy enough or perhaps there's an easier gadget to get the same effect? Perhaps for the 4 counts for 35mm for e.g., could I have 4 gates of some sort in series that close one by one, thus completing the circuit upon the 4th sprocket signal?
3) How to power and control the speed of the take-up motor, with 3 or so speeds? Also how to power and control the non-takeup motor.
4) BONUS if anyone here can help though it might be the wrong forum: Do you think I can get away with using a rolling shutter machine vision camera or do I really need a global shutter? Since it's only 3 or 4 fps, and i'm guessing the camera shutter can be set around 1/100th of a second shutter speed, and the film won't be moving
when the image is taken, I feel it should do the trick? Otherwise i'm looking at spending over double to get an equivalent camera with a global shutter.
Any thoughts would be great appreciated!
Cheers,
Mr.We
